Pellet mills conventionally employ a die ring in which individual ingredients or mixtures (feed material) are agglomerated by compaction in a die cavity defined by an annular die ring and rollers within the die cavity. The compaction causes the feed material to be extruded through openings in the die ring to form pellets which are discharged as the final product from the pellet mill. Rotating die rings are common, although stationary dies ring may be used. For example, see U.S. patent application Ser. No. 09/192,436, filed Nov. 16, 1998.
In certain applications, particularly for pelletizing a variety of different feeds, it is necessary to change the die ring. For example, the die ring may be changed two or three times a day for different production runs. Typically, each die ring has a die flange which bears against and is clamped to a mounting or quill flange formed on a frame of the pellet mill. The mounting and die flanges are jointly rotatable or stationary, depending upon whether the die ring is rotatable or stationary. Clamps comprising circumferentially extending ring segments each having a generally C-shaped cross-section with radially extending wedge-type flanges are typically joined to the mounting flange by bolts to maintain the die ring flange and mounting flange secured to one another. The clamping force is maintained by torquing down the bolts securing the clamp segments to the mounting and die flanges. Typically, the segments are bolted to the flange using three circumferentially spaced bolts.
While this type of clamp has proved reliable for clamping the die and mounting flanges together, certain problems have arisen. For example, when changing die rings, considerable time is required to remove each fastener and to handle each clamp segment. It will be appreciated that each clamp segment must be completely removed from the pellet mill to release the die ring. This, in turn, causes further problems. As the dies are increased in size, the die clamp segments become heavier and more difficult to safely handle. Moreover, improper torquing of the clamps sometimes causes non-uniform circumferential distribution of clamping forces about the flanges, leading to failure. Also, as the dies increase in diameter to handle greater loadings, the size and number of clamps increase which in turn increases the die changing time.
An Acme fastener was developed to decrease the handling time. However, only one such fastener could be used per clamp due to its radial position about the die. Each such Acme fastener included an externally threaded sleeve, a bolt passing through the sleeve threaded to the mounting flange, and a lock nut internally threaded to the sleeve and secured against axial movement relative to the clamp. This Acme fastener, however, proved inadequate and failures occurred. Accordingly, there has developed a need for an improved die clamp for releasably securing an annular die ring to the mounting flange of the pellet mill.